text:
Do aircraft have backup systems to trim when they don't have trim wheels?
What happens if the motor that trims the elevator of an airplane fails and there are no trim wheels in the cockpit (like in the Boeing 747). Is there a backup system or hidden trim wheels?

Yes, there is a backup system available when there is no trim wheel. On the Boeing 747, the stabilizer trim has two control modules, normal and alternate:

Stabilizer Trim
The stabilizer trim system provides pitch trim by varying the angle of
incidence of the horizontal stabilizer. Normal and alternate
electrical channels control two stabilizer trim control modules. Each
control module hydraulically powers a trim actuator. Actuator outputs
mechanically sum to drive the stabilizer. Trim rate is reduced at high
airspeeds.

(Boeing 747-400 FCOM 9.20.4 - Flight Controls - System Description)
While the normal trim is controlled via the switches on the yoke or via the autopilot, the alternate trim is controlled via two switches located on the center pedestal:

1 Stabilizer (STAB) Trim Cut Out Switches
ON - supplies hydraulic power for stabilizer trim.
AUTO -

supplies hydraulic power for the stabilizer trim
shuts off related system hydraulic power if unscheduled trim detected

CUTOUT - shuts off related hydraulic power to stabilizer trim.
2 Alternate (ALTN) Stabilizer Trim Switches
Push (both switches) - trims stabilizer in desired direction using
alternate control channel.

(Boeing 747-400 FCOM 9.10.2 - Flight Controls - Controls and Indicators)
All other Boeing aircraft without a trim wheel work similar.
On modern Airbus aircraft, manual pitch trim is usually not required because the fly-by-wire system takes care of that. These aircraft do not have trim switches on the sidestick. There is however always an alternate trim possibility. On the earlier models (up to A340), this is done manually via the trim wheels. Starting with the A380, the trim wheels were removed. There are now two pitch trim switches on the center pedestal for alternate control:

Controls the position of the Trimmable Horizontal Stabilizer.
It moves the THS at the following speed:

In clean configuration : 0.15 °/s
With slats/flaps extended : 0.25 °/s

The PITCH TRIM sw is composed of two switches, which are spring loaded to neutral. In order to move
the pitch trim, both switches must be pressed simultaneously. On
ground, the PITCH TRIM sw has priority over the automatic takeoff trim
setting. The PITCH TRIM sw is inhibited in flight, except in direct
law. (The auto trim function is lost in direct law. USE MAN PITCH TRIM
is displayed on the PFD).

(Airbus A380 FCOM 27 - Flight Controls - Pitch Trim Sw)
See also Why don't the A380 and A350 have trim wheels?


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By what measure was Gander International Airport the "largest" in the 1940s?
According to the Wikipedia article and the original source Gander International Airport

had four runways and was the largest airport in the world

by 1945.
Now, "large" can mean a lot of things, as in

the number of runways
the surface area covered
the total area or volume of buildings
the number of airplane operations or passengers (you would typically use "busy" then, but who knows)

but I'm not familiar enough with airport history to know which ones I would have to compare it to. LaGuardia for example was opened on Dec 2, 1939 and also had four runways.
So, my question is, by what measure was Gander the largest airport at the time (of course, assuming, that it actually was, by any reasonable measure)?

In 1938 when it opened, Gander Airport was at least 250 acres in size of graded land and it had 35 acres of paved surfaces. It's four runways used 1,230,000 square yards of concrete to complete. It was at the time the largest paved runways in the world.
Other than the 250 acres of level surface, I could find no information on the hundreds of buildings located at the airport. At one time this included a  USAAF air station, which was built after the physical airport was completed, with over 100 buildings for barracks, hospitals, hangars, warehouses and somewhere in the mix a fuel depot. There was an RCAF station located at the airport as well, which had a similar number of buildings. In addition, the Royal Canadian Navy had a communications outpost that was active through the Cold War. On top of that were 1700 civilians working at the airport. It needed the infrastructure to support hundreds of flights every day to get planes to the British Isles at the height of the war.
I think the size was considerably larger than 250 acres, but there's no data at all on the physical size of the airport. After the war, the churches, schools and libraries on base were donated to the town. It has about 175 acres available for lease if you are interested.

https://www.heritage.nf.ca/articles/politics/gander-base.php

Mmh, Berlin-Tempelhof was 4.5 km² of total area (1100 acres) in 1941, but had no paved runways, just one large grass field.

Are you claiming that the 250 acres of land made it the largest, the 35 acres of paved surface or the square yards of concrete? How does this compare to other airports of the time? @Raketenolli mentions Berlin-Tempelhof having a larger land area (but 3 years later).

@FreeMan The press and the airport claimed it was the largest in the world. I supplied information to better show why it was considered the largest airport in the world at the time. I think it's a combination of paved surfaces, thousands of employees, and land area. There was enough concrete poured just for runways and taxiways to build a 110 mile long two-lane road.

Gotcha. Thanks for the update.

99% Invisible contextualizes the importance of Gander:

By 1938, the Gander airport was fully operational but mostly unused. There just weren’t enough planes in operation that could actually survive the crossing of the Atlantic Ocean. In the two decades before World War II, only 100 planes had crossed the Atlantic — 50 others had tried and failed and 40 people had died in various attempts.

So, following the ferrying flights in WW2, prop planes stopped at Gander. That era came to an end with the jet era- the jet powered DC8 and Boeing 707 both arrived in 1959, the same year a huge renovated terminal was completed at Gander, resulting in a visit from the queen. Anyhow, that means some numbers are available.
New York Times, June 21 1959, GANDER SPREADS ITS WINGS:

handles an estimated 13,000 aircraft and about 250,000 passengers a year.

That isn't the most by volume, though. For instance, London Heathrow was serving a million passengers per year by 1953, New York's Idlewild/JFK was handling "nearly 3 million" by 1954.
Perhaps it was simply disproportionately large or important.
(H/T @niels for starting down this path)

Probably it was, just on the basis of the sheer number of planes arriving & departing per day. At that time, Gander was as close as you could get to destinations in Europe until they got planes capable of taking the polar route.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
What are the differences between FAA and EASA PPL(A) written exams?
Would studying for FAA PPL(A) written exam prepare you just as well for the EASA PPL(A) written exam, or is the knowledge base requirements (and study contents) significantly different in each?
I've found that PPL(A) FAA exam requires these below:
https://pilotinstitute.com/faa-private-pilot-written-checklist/
Regulations
Accident Reporting
Performance Charts
Radio Communications
Weather
Safe and Efficient Operations
Density Altitude Performance
Weight and Balance
Aerodynamics, Powerplants, and Aircraft Systems
Stalls and Spins
Aeronautical Decision-Making (ADM)
Preflight actions

and PPL(A) EASA, apparently requires these:
https://www.modularpilot.co.uk/how-to-pass-your-ppl-private-pilot-licence-theory-exams/814
Theory / Fact Learning Exams

Air Law
Operational Performance
Human Performance and Limitations
Aircraft General Knowledge
Principles of Flight
Communications

Practical / Fact Learning Exams

Meteorology
Navigation
Flight Performance & Planning

Just doing a quick glance comparison, the requirements seem to vary.
I was considering an online resource that has good review (Sporty's ground school) but I want to know if this resource would even be compatible for preparing for the EASA PPL(A) exam (since I live in Europe).
Thanks

In Europe you should have access to relatively affordable training through an aeroclub, at least from my experience in France and Germany. Why not get a book or other EASA materials and take classes at your club?

Thanks for the info @Raketenolli, I am a newbie at this and had no idea there was that option. I will look for aeroclubs here in Spain. My ideal scenario would be to study on my own and take the exam when I'm ready, but apparently, at least from what I've read, in Spain, a school needs to 'recommend-approve' me as 'ready to take the exam' so I can then register to take it exam. I'll contact AESA here in Spain to see if there are workarounds for that. Thanks again

This is a great question. Another way to ask it is whether someone who has recently studied for and passed one of them can "top off" their knowledge with a brief evening review of major FAA/EASA differences and expect to pass the other or whether they would have to go back and learn entirely different concepts, techniques, etc.

It seems a good starting point to finding a suitable club is https://realaeroclubdeespaña.org/aeroclubs-2/ From my own personal experience, doing theory (studying) and practical training in parallel works best, just because you can more easily relate the two and applying what you learn helps you retain it.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What's actually a DISPATCH MESSAGE in A350?
I am new to this community. I have been reading a lot about ECAM. I just got stuck and didn't quite understand what a DISPATCH MESSAGE is.
What is the difference between DISPATCH MESSAGE and MEL? Thank you.

Could you include a link where you read about this message, for context?

Few definitions to get on the right track:
ECAM (Electronic Centralized Aircraft Monitor) is an onboard system on Airbuses that monitors status of aircraft systems. The most famous(?) feature of ECAM are the checklists it displays in case of a system failure, but the system has also other features that help crew to build their situation awareness and to review aircraft's current technical status and capabilities.
MEL (Minimum Equipment List) is a part of the aircraft's Operations Manual. It defines the conditions for the commencement of the flight in case of a system failure.
The A350 introduced a new feature in the ECAM system called "Dispatch Messages". Dispatch messages are a list of system failures that affect the departure of the aircraft (aka "dispatch"). They are displayed on a dedicated DISPATCH page of the ECAM system.
The purpose of the feature is to let the flight crew quickly and correctly identify any failed equipment that may affect the departure of the aircraft. The crew can then find the correct procedure from the MEL. Indeed, it is not always easy to define what actually has failed as failure in any of the components in a subsystem may render the entire system useless. The dispatch messages help flight crew to identify the failed component while the associated ECAM alert and procedure guide the crew on how to secure the failed system. Depending on the actual failed component, the aircraft may be able to be fly again or it may require some maintenance before the next flight.
The MEL of A350 has an index of dispatch messages so flight crew can quickly find correct procedures. Moreover, the Onboard Information System (OIS) detects any dispatch messages providing a direct link to the correct page in operation manuals, including MEL.
If the failure itself requires immediate crew action, the Dispatch messages may be accompanied by an ECAM alert and an associated checklist but they may also appear on their own. In such case, a "DISPATCH PAGE UPDATE" ECAM alert is displayed guiding the flight crew's attention to the DISPATCH PAGE.
Besides serving as a tool to determine aircraft's airworthiness before departure, The DISPATCH PAGE can also be viewed in flight so that the crew can assess the technical status of the aircraft to support their decision making considering the upcoming flights. For example it may be required to return to the base for maintenance if the destination does not have maintenance crew or spare parts available, even if the actual failure does not have direct effect on the current flight.

Thanks for the explanation. Very informative.


text:
Why is the fuel:air ratio of a turbojet engine not around ~1:15 (the stoichiometric ratio)?
Also, what is the maximum fuel:air ratio possible in a combustion chamber of a jet engine?

Would you please provide some sources for your information?

I think this question should be rolled back, the latest edit of ditching the f/a ratio of 1/4-1/3 totally changes the question. As it stands now, this is a very good question, but it is not what Call Me Dosya asked originally.

If one would take a look at the %fuel/air combustible range for Jet A1 kerosene (Engineering Toolbox), it is around 0.7 to 5%.  So 1/4 to 1/3 would be way too rich.

Edit: to honor my original answer, I shall keep it as it is. The question was edited so much I think it would have constituted a whole new question. In it's original form, the Q presented jet engine f/a ratio as 1/4 - 1/3 and compared it to the stoich ratio of 1/15.
Your numbers seem way off, except for the stoichiometric fuel/air ratio (for kerosene).
Please see the following NASA article: Beginner's Guide to Propulsion and EngineSim
Fuel and Air Relationships
Activity
A quote from there:

For jet engine combustion, the important parameter is the fuel/air ratio (f/a) which is the ratio of the mass of fuel to the mass of air being burned in the engine.

The stoichiometric ratio of 1/15 can also be written as approximately 0.067
The article further elaborates on the subject:

For example, at sea level an airliner taking off at 375 mph with the throttle at 100% has an f/a of .017

This 0.017 translates into about 1/59
No matter how you look at the ratio, mass or volume, in no case will a jet engine run at f/a of 1/4~1/3. The mixture will simply be too rich to ignite and burn.
Here is a link to a Wikipedia graph about the range of typical jet engine air:fuel ratios:
Combustion stability limits of aircraft gas turbine.svg
Please note the graph displays the ratio in reverse order from what was used before in this answer, ranging from ~25/1 to ~180/1.

We have to remember air is only 20% oxygen.  When you write the stoichimetric formula for the chemical reaction (using oxygen) on a molar basis, you get the combustion ratio by converting the fuel and oxidizer from moles to mass.
To get the combustion ratio using air, you divide the oxygen mass by its fractional proportion in air.
Interestingly, the stoichimetric fuel/oxygen ratio (by mass) is around 1:3. 3 divided by 0.21 gives us around 15 for kerosene and air.
Turbojets burn fuel in combustion "cans" within the flammable fuel/air percentage limits and use the heat from that combustion to warm more air passing through the the core.
Bypass fans can make these ratios even higher.  For example, the Ge 90 has a bypass ratio of 9 to 1.  Of the 10% of the total air mass flow going through the core, its air to fuel ratio is around 33 to 1, much higher than stoichiometric.
The total air to fuel ratio (by mass) is 330 to 1!
One can see why fuel combustion "cans" were invented, and why fan jets are becoming more popular.

When calculating a/f ratio, you can not take into account the bypass air. It is the same as if one would calculate the a/f ratio of a propeller acft and count into it the air the propeller is moving

@Jpe61 that is true.  The total air moved is interesting.  Prop thrust may be more related to its lift that "air moved".  More to write about.

Lift is pretty much the air moved.


text:
Please describe ram pressure in simple terms
Please someone describe the following sentence in simple words:

The Airspeed Indicator is calibrated for 'standard' sea level density, so it will only read TAS if the density of the air through which the aircraft is flying is 1.225 kg/m^3.

Welcome to Aviation.SE! Can you edit your question to include what you already know about airspeed indicators?

Or this one as well: https://aviation.stackexchange.com/q/7500/7532

Airspeed is basically measured by measuring the kinetic energy of the air molecules impacting dynamic pressure port (for example on a pitot tube).
The higher the velocity, the more energy, hence more pressure, and higher speed indication.
If the density of the air is changed while speed remains the same, the energy will change. If the air is denser, for example during high ambient pressure weather, there will be more molecule impacts, higher pressure, and the indicator will show higher than actual true airspeed reading.
If the air is less dense, like when flying higher, the opposite happens: while the true airspeed is the same, there are less molecule impacts, less energy, less pressure, and the indicator will read lower than normal.

I find extreme examples useful when trying to keep things like this straight in my head. Your air speed indicator will read too low in space and likely too high in water.

Remember that an airspeed indicator is a simple differential pressure gauge.  It reacts to a difference between static pressure and ram (stagnation) air pressure.
Static air pressure is just the pressure exerted on air within our atmosphere at a certain altitude by the weight of the air above it.  Gravity is constantly pulling all the molecules of our atmosphere toward the Earth, which compresses the gas against the Earth’s surface.
Static air pressure increases the lower in the atmosphere you are and decreases the higher up you are.
Ram air pressure (scientific term is stagnation pressure) is air pressure which is the sum of both the local static pressure as well as the pressure created at the boundary layer from a change in momentum of the air.  Put simply, an object moving through the atmosphere is forcefully pushing the atmosphere out of its way and this exerts a component of pressure on the air as well.
Since an airspeed indicator works by simple manometry, it needs some means to correlate that differential pressure change to an analogous pressure it would experience if the gauge was sampling at a particular airspeed.  Manufacturers typically calibrate an airspeed gauge to accurately display airspeed at sea level in SI standard atmospheric conditions.  So if a pitot tube is sampling dry air at 101.5 kPa, 15° C, the indicated airspeed reflects the actual airspeed.  But since the air gets thinner with altitude, temperature, moisture, etc the actual airspeed will be higher in those conditions than what is indicated by the airspeed indicator.  This is the difference between indicated airspeed (IAS) and actual or true airspeed (TAS).

The airspeed indicator is based on ram pressure for a very good reason: because the wings need to deflect a certain mass of air in a certain amount of time to generate lift to support the aircraft.
When the aircraft is higher, the air is thinner, but the aircraft mass is more or less constant$^1$.  In order to deflect enough air to maintain lift, the aircraft must move faster.
The pitot tube works the same way.  The plane must move faster when air is thinner to collide with enough air molecules to increase pressure in the tube equally to a slower speed in denser air.
This is why True Air Speed increases relative to Indicated Air Speed in air of lower density.
$^1$ the plane does get lighter with fuel consumption

And not just the lift on the wings!   Everything aerodynamic that happens to a body in motion in a fluid is dependant on the change in momemtum (the force), of the fluid particles impacting and deflecting from the surface of the body.

Ram air pressure is simply the airflow pushing against an object.
Imagine travelling down the freeway at 75 MPH.  You open the window and stick out your hand.  That pressure is ram air pressure.
The airspeed indicator takes that ram air pressure and subtracts out static air pressure or what you feel when the car is not moving.  (You do feel something but may not realize it as it is always there).
The difference between ram air pressure and static air pressure is read on the airspeed indicator.

ASI’s are calibrated so that IAS = TAS at sea level on an ISA standard day.  As you increase altitude the air becomes less dense so to indicate the
same IAS the TAS has to increase to produce the same dynamic pressure measured by the ASI.

Please someone describe the following sentence in simple words

The higher you go, the thinner the air is.²
The Airspeed Indicator is calibrated for the 'thickness' of air at sea level. At higher altitudes, it will give 'wrong' readings, and not show your actual speed (TAS, True Air Speed)

² = Air being thinner means if you have a 10 liter box at sea level, it will contain "more air" than it will at 10,000ft altitude.


text:
Effect of velocity of air on stagnation pressure
Why does stagnation pressure remain unchanged when velocity of air increases if the formula is:

stagnation pressure = static pressure + (1/2×density×velocity$^2$)

jfksgya.  Does it?

The formula you cite is for incompressible flow, such as liquid or very low speed gas flows. If no work is done on the fluid the stagnation pressure remains constant so increasing velocity will decrease static pressure (and vice versa). Flow through a pipe that gradually changes diameter would be an example (though we do need to neglect friction losses).


text:
ICAO ATPL Conversion to Transport Canada
I am a former Captain for PALExpress, an airline in the Philippines. I have a valid CAAP ATPL and am rated for the DHC8-400 and sadly was part of the retrenchment program for Philippine Airlines last February 2021. I have roughly 2800 hours on the DHC8-400 and I am currently located in Edmonton, Alberta and would soon be petitioned to be a Permanent Resident here in Canada soon. I am currently looking into transferring my valid ATPL license into a Transport Canada license as I would love to still try and pursue a career in aviation.
I would just like to gather any information in this forum I could use on this topic. I have sent a couple of emails to local flying schools in the area and also to Transport Canada and have received responses from them. Regulations state that I would be required a valid Class 1 Medical Certificate along with my license, and would have to complete a couple of exams and a skill test for the conversion.
My concern is that I do not have a valid Class 1 Medical certificate with my ATPL and also am not current. Does Transport Canada require me to have a medical certificate that is issued by the same issuing authority of my license, or would I be able to apply for a Class 1 Transport Canada medical for this purpose? Also I am currently rated for the DHC8-400 only and would not be able to do recurrency on the aircraft cause of the possible expense it would cost. Would it be possible for me to be trained and then be rated by a TCCA Check pilot, for a Multi-engine aircraft that could be used for the skill test? Or would I have to get current and get an aircraft rating from the issuing authority of my license?
I was wondering if there are other people here who have gone through the same thing about and would love to hear your story as to how you got back to flying. Any information and help in this matter is well appreciated.
Safe Skies everyone, Thanks!

Welcome to Canada. TC's foreign pilot licensing conversion requirements are here. TC expects you to have a medical from your home authority but they don't say it needs to be current.  In any case, you'll need to get a Canadian Cat 1 with a CAME (Canadian Aviation Medical Examiner) here, so go do that right away.  Expect a delay getting paperwork because of the Federal Government you-know-what protocols has really slowed everything down, so the sooner the better.
You also will have to do the SARON, SAMRA (ATPL) and INRAT (IFR) exams. The ATPL exam requirements in Canada are much lower than the EASA I am told (numerous exams for the EASA ATPL vs only two in Canada), so not so bad in comparison.  I don't know why they include the IFR exam, since much of the content is duplicated in the ATPLs. I guess they want the maximum amount of the basics covered.
Start studying for the exams, and I recommend taking an ATPL seminar given by several companies that do so (they are mainly side hustles done by airline pilots - I attended both an INRAT and ATPL seminar and really enjoyed them and they will improve your exam mark quite a lot, plus you get a bit of networking contacts going - it's a very "small world" in Canada).  It'll depend on how good your existing knowledge base is relative to Canadian requirements and that will become apparent when you start to self-study for the exams (for example, a lot of the material relates to flying and navigation in the far north etc, which I'm sure is a new thing for someone coming from the tropics).
The skill test is the Multi-engine Instrument Rating check ride (unlike the US, in Canada you have to do your IFR ride in a twin to fly twins in instrument conditions). During the Multi-IFR ride you will shoot an ILS and Non-Precision Approach and do a simulated engine failure on an NPA missed approach, while under the hood (it's usually on the non-precision approach so you aren't doing zero thrusting engines close to the ground).
So, you'll need to go to a flying school like a newbie, get checked out in their multi-engine trainer (like a Seminole), and do as much as possible as sim time if they have one of those basic motion simulators like the Red Bird to save a few bucks. So the amount of time and money is going to depend on previous experience in the trainer they use, your own sharpness after being off-line, differences in country related procedures, etc. Figure on a total cost maybe between 2-5k for a few hours in a twin and sim, study guides, and all that.
Don't worry about your type rating. An employer that hires you will take care of recurrent training if you're hired for D-8s, or an initial course as applicable if you're hired for RJs or some such and it's a new type, so the only major expense will be for the light twin and sim time and the training materials.
And of course, make sure your logs are up to date and all that.
I don't think that after jumping through all the hoops you'll have too much trouble getting a job with your experience, as the industry slowly ramps up, because there was a fairly severe shortage of experienced pilots before all the crazy business happened (Jazz is recalling pilots on furlough, and a friend's very-low-time daughter who had just started flying there, then went on layoff in early 2020, is going back to do recurrent and return to the line on the 400).
Good luck!

Thanks so much for answering John K! I'm hoping to get to do the exams as soon as I get my spousal sponsorship approved so I can get to training for the Flight exam as soon as I can.
Do you think that my currency would be an issue with the conversion? Would I still be able to get a certification to fly to train here in Canada? Also would my current rating be enough to fly a multi-engine aircraft here, even though I am not rated for it? It works differently in the Philippines, because you need to be rated for each aircraft that you fly, yes even if its just a C172 even if you fly the Airbus.

Currency would be taken care of by virtue of meeting the Can requirements. For the purpose of the Can ATPL, I would say you are current by virtue of passing the exams and a multi-IFR checkride and TC issues you a Cdn ATPL.  The multi-ifr is a basic part of the ATPL, so you if you have it, you can fly whatever you want, only subject to type rating requirements on a/c over 12500 lbs.  You need to find a flight school you like and go have a chat.

Thank you so much for the information! Do you have any recommendations on where to find seminars in regard to the examination subjects? You have been so kind and helpful, I cant thank you enough for it!


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Does ATC expect 250 KIAS during vectors for an instrument or visual approach?
During vectors to an instrument or visual approach does ATC expect the pilot to maintain 250 KIAS until cleared for the approach or instructed to slow to another speed?

Be aware too there are many airplanes in the sky that can't even come close to 250 KIAS. As I recall, the fastest plane I ever got checked out on had a Vne of 164 KIAS, cruise speed of about 130 KIAS, and I'd usually fly an instrument approach at 90 KIAS.

Generally no, we do not expect pilots to stay at 250 until final. That would be very fast.
Of course I expect the pilot to slow to 250 indicated (which will show as 270-280 over the ground) when reaching 10,000 MSL. And then I will expect further speed reductions as the aircraft gets closer to the airport and the pilots run their checklists and begin configuring the aircraft for landing. Where I work now we very rarely have to use speed restrictions, and I would guess that most jet aircraft are doing around 180-220 on the base leg without any instruction from me.
Military fighters will sometimes stay quite fast on the base leg, sometimes 250+ knots over the ground. This is not normal for other aircraft.
When I was in radar training with the FAA, in the simulator sessions the general rule of thumb was to assign 210 knots on the downwind, 190 on base, and 170 on final. These were slower on downwind and base than the aircraft would otherwise fly, and faster on final. But that was only simulation.
At busy airports where there is a constant stream of arrivals it is very common for aircraft to be assigned specific speeds, whether over the frequency or via a published procedure.

The 7110.65 says this (paragraph 5–7–3):

When assigning airspeeds, use the following:
c. To arrival aircraft operating below 10,000 feet:

Turbojet aircraft:

Assign a speed not less than 210 knots, except for the aircraft as specified in subparagraph b above [operating below a Class B shelf], or
Assign a speed not less than 170 knots when the aircraft is within 20 flying miles of the runway threshold.

Reciprocating and turboprop aircraft:

Assign a speed not less than 200 knots, or
Assign a speed not less than 150 knots when the aircraft is within 20 flying miles of the runway threshold.


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How to find the velocity of the working fluid through the fan in a turbofan engine?
Is there any formula for the velocity of the working fluid (air) through /the fan of a turbofan engine? If not, how can I find the velocity?

here is how to get an estimate.
At cruise conditions, the airflow into the engine is such that (ideally) the circumferential lip of the inlet shroud is a stagnation point in the flow- that is, no part of the inlet flow spills out and around the engine nor do the streamlines of the inlet flow converge outside the inlet before entering it.
This means that the inlet ingests all the air coming at it at cruise. If you know the velocity and density of the entering air and the bypass ratio, you can solve for the mass flow rate of air through the core of the engine.


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TruTrak Vision PMA Autopilot Limitations for coupled instrument procedures- C172M - STC SA04231CH
I am currently flying a Cessna 172M with a TruTrak Vision Autopilot installed under STC SA04231CH.  Section 2.4 of the approved AFMS states:

This autopilot has not been evaluated by the FAA to meet the
certification requirements for coupled instrument procedures,
including coupled approaches. Therefore, these types of procedures are
not authorized without further evaluation and approval.

The remark concerning "coupled approaches" is clear.  However, does "coupled instrument procedures" remark mean that the autopilot is essentially a 'VFR operations only" system?  My IRA check ride is coming up soon and I'm trying to understand what I can and cannot use the autopilot for, and therefore what I can be tested on.
Thank you for any comments.

I don’t have an answer for you.  But I would definitely reach out to Honeywell/Bendix-King, as they acquired TruTrak a few years ago.  Or your avionics shop.  You really need to know the answer prior to your check ride.  You need to fully understand the IFR applicability of every system in the panel and be prepared to discuss with the DPE.  He or she will not be OK with “I’m not sure so I’m just not going to use it for approaches.”

(Continued) Remember too that a flight control system is really the combination of the GPS navigator, Attitude Indicator, HSI/DG, and autopilot.  It is an approach capable autopilot so my assumption is that your plane has a GPS, or AI/HSI that are unable to support vertical nav modes.  You may still be able to use it in HDG mode to fly holds, and in NAV mode to track a radial with altitude hold.

Thank you, Max. This is helpful. The aircraft does have a GNS 430W and is capable of LPV approaches. I’ll reach out direct to Bendix-King tomorrow.  Much appreciated.


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What is this biplane from an old photo?

Can anyone identify this biplane.

The tail number under the wing appears to read "NC12..." or "N612..." perhaps?

@abelenky It’s a C. “A second letter indicating the aircraft's airworthiness category followed the N and preceded the identification numbers. These airworthiness indicators were; "C" for standad, "R" for restricted, "X" for experimental, and later an "L" for limited, (for example, NC1234).”https://www.faa.gov/licenses_certificates/aircraft_certification/aircraft_registry/aircraft_nnumber_history/

I'd tend to think it's a variant of the Laird Swallow with another engine, perhaps NC1236. Here are the 3-figure ids, and here the 4-figure ids starting with NC12.

@mins don't forget the 5-figures ids

Definitely NOT a Laird Swallow, which is far too early a design with to have many of the visible features.
It is instead a Great Lakes 2T-1A sports trainer - a rather well known aerobatic aircraft, of which quite a few are still registered, although most of the survivors don't have an upright inline engine (horizontally opposed replacements being a popular replacement). Their logo is even visible on the fin.
Airhistory.org lists two batches of aircraft with potentially matching registration numbers in the NC12nnn range including NC12845, NC12846, NC12847, NC12848, NC12887, NC12889, NC12890, NC12891 - all of which also match the unknown third digit - and which actually have enough digits to match the smear on the tail - which is clearly not a 3 digit serial.
I have attached an image of a similar aircraft below.

and the company's logo:

From what I have seen (I put in some screen time), I'd have to agree with mins that it appears to be a variant of the Laird Swallow. There are 5 Swallows on the registration list between 1236 and 1297. The small bit of the third number makes me think that it is a 6 or a 9, and I'd probably guess a 9, which would make it NC1297, assuming, of course, that it had a 4 digit reg number. NC1297 is a Swallow, last registered to Orin Welch Aircraft Co of Indiana. Swallows were manufactured with several different engines, so the odd cowling isn't much of a concern.


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What are specified rudder pedal forces?
Zeus have previously provided us with links to aviation certifications standards (e.g. FAR 23.155, FAR 23.397).
I think Far 23.155 specifies the forces to provide maximum elevator control signal. But I do not find the same for rudder nor Aileron. Far 23.397 do specify higher values, but it seems like forces that might happen on more manual controls.
I just tried a simple test setup with person weight and sitting in a chair, and I am a 85 kg. male. I think it gets uncomfortable to press more than 45 kg or (100 lbs) with one foot. A smaller (female) person may not like that.
If you design a force sensor in a pedal for rudder, what is the design limits according to these standards? What should be considered max signal?

FAR 23.143 used to limit the short-term maximum rudder pedal force to 150 lbs-f (670 N) and the maximum for long-term to 20 lbs-f (90 N). For gliders (JAR 22.143) these limits are 400 N and 100 N, respectively.
MIL-F-8785 B (§ 3.3.2.5) used to limit the rudder pedal force to maintain coordinated flight to 50 lbs-f (220 N). § 3.3.9.1 gave a maximum limit of 180 lbs-f (800 N) in case of unsymmetrical engine failure.
All these standards are no longer enforced, but they were the result of years of experience and still give good advice. I would expect that you will see much higher short-term loads, so your force sensor should cover the range from 0 to 300 lbs-f (1330 N) on a single pedal at least. Don't disregard dynamic loads and the force people are able to produce when under stress.

Thank you for this information. This provide you information on the maximum loads an airplane MAY require the pilot to press on a pedal and structural design limits. I have been a glider pilot, and I remember that only small forces on pedal was required in any case. Regarding elevation control the standards require minimum forces, that is required for a max control signal. In this way the pilot get an ergonomically (proprioception) feed back on how hard the pilot try to influence the airplane. But as I see this, standards require no minimum forces for pedal and yaw control.

@Backflip Yes, there are also minimum forces. You need a positive gradient and MIL-F-8785 has a minimum friction of 1 lb. For practical purposes, you need to signal to the pilot when the structure is overloaded. Glider rudder cables are run in PE tubes to give the mechanism more friction.

Thanks. I found a readable copy of Mil-F-8785 here and will start to read :) https://archive.org/details/DTIC_AD0738625/mode/2up
You seem to indicate, that you need friction force for the motion of the rudder. So there is no proportional relationship between force applied and "influence on airplane" (I hope my term makes sense).

@Backflip A bit of friction is helpful for damping. Generally, a linear relationship between cause and effect is desired and asked for in the regulations.

The regulations prescribe forces that can comfortably be maintained during required periods of comtrol, by a representative pilot. But if the design is for an installation, it should be able to accomodate for the highest load that can be expected, without mechanical failure. An 85 kg person standiing on one leg can maintain an 85 dN load for a while, and even jump up and down on it.

Above pic is from this answer, and depicts actual measurements from multiple test persons - what the human max forces are over time, per flight control. It is from prof. Gerlach’s uni book I held on to.
You can see the variation in force and endurance, particularly with the pedals. The force sensor must be able to handle the maximum force, times a safety factor of 2-3. The forces achievable over a couple of minutes would be of interest for the regulations, the impact forces at t=0 are much higher and it would not be good to have the sensor replaced after every kick.

Thank you for this information. This will provide you information about maximum forces humans can deliver on pedal. Regarding elevation control the standards require minimum forces, that is required for a max control signal. In this way the pilot get an ergonomically (proprioception) feed back on how hard the pilot try to influence the airplane. But as I see this, standards require no minimum forces for pedal and yaw control.

The regulations are concerned with the right hand side of the graph: stay below the line of what humans can maintain comfortably. The mechanical set-up and force transducer should be able to handle the left hand side. Proprioceptive pedal feeling can be taken proportionally to the graphs, @ 10 mins pedal forces are about 3 times as high as yoke forces. The plots we took for simulator force control always showed higher static forces on the pedals.

In a way the rudder signal comes from a difference in forces to the two pedals. But I guess that when pilot want about max effect, then the pilot do not press with the other foot. So a design signal (force) range for an "electronic pedal" could be 0 - 25 daN. And then of cause it shall be able to withstand higher values.


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What downsides could there be to not letting your engine's oil temperature get above the given limit to taxi/take off before you do so?
I'm not a pilot, and I'm sure most pilots who fly piston aircraft would know this, but what could happen if you operate an aircraft with an oil temperature lower than what the checklist says you should have to taxi or take off?
This may be specific to radial engines, I'm not actually sure. The only plane I've flown in (and remember waiting for the oil temperature to rise) was a Howard DGA-15 with an R-985 engine. We waited for the temperature to get above 90 Fahrenheit before we took off.

I was in a rotax 912 today. You are absolutely not supposed to raise the throttle until the oil temp hits 120F. On a cold not freezing day that's 5-10 minutes.  Though I suppose nothing's stopping you, aside from the FADEC logging all data.

Could you rephrase that? Aren't the differences between down- and up-sides more important?

There's some great answers below, but a simple way of looking at it is basically for all the same reasons that we used to need to do this for cars - aircraft ICE engines are far slower to be modernized due to stringent (expensive) regulations. With all the other pre-flight preparations going on, optimizing the time for the engine to be ready is quite low on the list of priorities for manufacturers/customers, whereas for a car this is decently high as a priority.

This is to ensure that the lubrication properties of the oil are sufficient. The viscosity of motor oil, or any other oil for that matter, depends on the temperature of the oil.
If the oil is too cold for its rating, it will be too viscous (thick) and will not meet the requirements for lubrication as engine power is increased.
While there may be oils that would work well under colder temperatures, these may not be approved for the engine(s) in question, hence the minimum temperature limit.
Oil temperature is also a good indicator of the overall temperature of the engine core, and it is generally not advisable to strain a cold engine. When the said oil temperature has been reached, it is safe to assume the engine itself is also sufficiently and uniformly warmed up.
The problems that may arise from not adhering to the temperature requirement are increased engine wear, lower power output, and increased fuel consumption. Extreme cases may result to engine damage, even a catastrophic one.

Another downside of oils specified for a lower operating temperature is their performance at the top end of the temperature range, if they get too thin

…and if the lower power output is not enough for lift-off, that may also lead to catastrophic damage.

True on both accounts, however, modern multigrade oils would easily cover pretty much any conditions, but they might otherwise not be suitable (and/or approved) for a/c engines, and the engine temp aspect remains. Very old engines may be very picky about the oil, requiring perhaps even additives such as zinc, but I think this is beyond the scope of this question.

@Jpe61 multigrade oils would indeed be a solution but as both the design and regulation of aero engines is very conservative. Piston engine designs and even actual engines do last quite a long time after all

The main downside is you can starve pressure-critical items like main bearing journals from adequate pressure to keep metal from touching metal when the bearing load is at the maximum (in the case of plain bearings - roller and ball bearings are lubed by spray and not sensitive to pressure as long as the oil is present).  If the journal surface touches the soft babbit bearing material, material transfer occurs and the breakdown process starts.  Maybe 50 or 100 hours later, the breakdown is complete and it throws a rod.
Lubricating qualities are a factor, but the main issue is oil flow and the effects of viscosity, being higher at low temperatures, on flow, which affects local pressures.  You are pumping oil through a network of passages and galleries that get progressively narrower as oil is branched off to feed different parts.  If viscosity is excessive, oil tends to "back up" more at restriction points, and pressure on the upstream side is too high, and pressure on the downstream side is too low. You could say that the oil distribution network is "tuned" to function with a specific pressure range and viscosity.
If viscosity is out of limits on the high side, you end of with different internal parts of the oil network where pressure is higher than the gauge indication and other parts where it is significantly lower (more than the normal variability).  If bad enough, some components may get starved of oil, and other areas subjected to too much pressure may start to leak, or even, in the case of oil lines and coolers, rupture.  Plain main bearings, that have to directly transfer the force produced by the combustion stroke to torque without touching, are most critical part of this, although everything is affected to some degree.
The temperature of the engine itself isn't that important, except for perhaps cylinder heads.  Lycoming's operating policy is, if the oil is in the green and the engine can take full throttle without stumbling, it's warm enough.
Also, if you are using multigrade oil like Aeroshell 15W50, you have a lot more latitude and going to a high power setting while below the green on temperature, on an engine designed to use straight weight winter oil like a 60 weight (equivalent to SAE 30), is much less likely to damage anything.

+1 I have an buddy who has a severe mental condition that leads him to collect old italian cars. Whenever he offers me a ride in one, after engine start we wait for a minute or two for the oil pressure to drop, which is a sign of the oil warming up sufficiently to flow properly.

I use Aeroshell SAE 15W50 in my Lyc O-290 powered homebuilt and it affords the luxury of treating the plane more like a get-in-and-go car in all weather.  It doesn't really need preheat unless the ambient temp is down in the teens F.  It has a weird characteristic where the pressure will drift down to the bottom of the operating range during cruise (50-80 psi) maybe go slightly below (not a problem at 55% power) if the oil quantity is below about 6 quarts, even though the temperature is normal.  I don't know how the suction pickup is able to tell how much oil volume is above it.

another consideration is that, the oil system has a max operating pressure. when the oil is cold, the viscosity is higher.  when you rev the engine above idle, the pressure will build quickly b/c the oil doesn't flow past the bearings well, (viscosity too high).  this high oil pressure could blow out seals, which leads to oil loss & then catastrophic engine failure.

It may also rupture the oil filter, possibly releasing particles back into the circulation.

Another thing not mentioned.
The high oil viscosity when cold can lead to high pressure drop and cavitation on the  oil pump suction side resulting in low and unstable oil pressure.
Vedeneyev M14P suffers from this.


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Thinking of investing in getting a commercial or instructor license but having a hard time evaluating the current job market as an outsider
I really appreciate your advice on this one and please excuse my ignorance. I already fly gliders and am passionate about aviation like many of you here. I work in software, but sometimes get fed up with being inside glued to the computer all the time and would love to find some part-time in aviation. My goal, however, is not to go to the airlines. I'd like to split my time 50-50 between coding and flying. The airline pilot lifestyle doesn't seem like it's for me and I still love writing software too.
My question is, if I invest in earning a commercial or instructor license, do you think it'd be worth it? Simply put, does it seem like job demand is getting better or worse mid-to-long term? Are a lot of you guys struggling right now with demand in the job market? I'm thinking of potentially flexible jobs along the lines of tours, instruction, search and rescue, firefighting, etc...
I'd even be willing to accept a bit of a decrease in income (compared to just doing software) if it meant getting to fly at least a few times per week.
Pursuing aviation to this degree would mean pulling funds I've saved for long-term investments I've made in the market (which you're not supposed to touch!), so it's a big decision for me.
Thanks for your tips!

Voting to keep open. Market research is an actual thing.

Problem is part of the question has a concrete (to the extent one can be given) answer, that Koyovis has responded to, market conditions, but part of it requires a personal value judgement.  It would probably be better as simply "what is the jobs outook for part-time pilots"? and leave it at that.

Own work, from a Jan 2020 presentation
The long term might be looking good. I was involved in market research for civil flight training: before covid, the market showed 5% average growth per year, with temporary setbacks that were fully compensated for in subsequent years. Even in beginning 2020 there was a structural shortage of flight training capability projected for the near future.
Worldwide, covid is the largest and longest setback of all. We’re still in a recuperating phase, with here in Australia for instance ex-pilots driving trucks. It will be a while before the market will be fully restored, but growth in flight training is projected to be up to 15%.. Admittedly, from a low base.
Is it worth investing money into this? Purely financially speaking, perhaps not, salaries were under pressure from the low cost airlines. For filling out life experience with responsibility and adventure: definitely.


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Does Headwind on Landing affect Ground Effect?
I am currently training for my commercial Pilot check ride and I am trying to execute the short field spot landing.  Under FAA ACS standards you have to hit your spot within -0 to + 100 feet.  I live in New Mexico USA where the winds can be quite unpredictable and I am having a hard time knowing where to aim to hit my spot.  It seems that with a sizeable headwind the airplane does not want to float as it would if there was not any wind.  In fact with a 15 knot headwind it seems like the plane does not want to float at all, almost like ground effect isn't there.
My understanding of ground effect is that it is basically the planes wake being reflected back to the wings creating a high pressure area under the wings and consequently increasing lift.  However, if there is a headwind when landing, wouldn't the wind blow the wake of the aircraft away from the wings and reduce ground effect?  Reversely if you have a tailwind wouldn't that blow the aircraft's wake further under the wings?  That would explain why a plane seems to float forever when landing with a tailwind.

When you say when there is a headwind the plane "does not want to float", are you speaking of a reduced "float" time, or a reduced "float" *distance"?

As Robert stated at the end of his answer, practise makes perfect. To me it seems you just haven't got the hang of it, put more hours into it and you'll get it. The reluctancy to float is due to the gradient effect. You are losing airspeed as wind dies going down, it always does. You need to aim differently depending on wind, and ATIS will give you the wind.

One thing about New Mexico is alot of it is a mile or more high.  So you're dealing with greater TAS from altitude too.  As far as the glide path (which you can get as good as possible without "resorting" to throttle or flaps/slipping)  you aim long for a headwind but less "float" distance.  Tail wind is opposite.  Maybe the mind confuses distance with time a little when floating.  But I would bring someone along to help with IAS.  Invariably, if you round at the same IAS, you go farther down the runway with a tailwind.  Time never seems the same with a little adrenaline going.

ground effect is that it is basically the planes wake being reflected back to the wings No, that is a misunderstanding. When calculating ground effect, a second wing is positioned such that it looks like a reflection of the real wing in the ground plane. This is a trick to achieve a flow pattern where streamlines at ground level are parallel to it. What really happens is that downwash is reduced because it is blocked by the ground.

There is no need to aim at a different spot on the runway based on wind.  Aim where you intent to land, period.  Just anticipate needing more power to stay on glideslope the stronger the wind is.  "wouldn't the wind blow the wake away..." sure, at the same speed and direction it is blowing the airplane for a net zero difference.

What you have described may be a gradient effect.  When descending in a headwind, windspeed can be considerably lower near the ground than at 100 feet.  If it is possible (perhaps with your co-pilot) monitor airspeed all the way down.  Make sure that, even though groundspeed looks the same, you are not losing airspeed due to wind gradient. Short final and rounding are busy times.  You could lose 5-10 knots IAS without even realizing it.
This will depend alot on local knowledge from experienced pilots.  If the terrain and wind direction favors a gradient, you should know about it before getting too "cute" with short field technique.
It would really help learning to hit the spot rather than trying to shave a few knots off the approach. A lull, or gradient, could put IAS dangerously low.  Descending into a gradient, one must pitch down to maintain airspeed.  This will put your target in a different spot in the windshield.  The pilot may try to keep the target in the same spot, resulting in a pitch up and loss of airspeed.  The downwind case is of course opposite.
There are 2 good ways to "hit a spot" in wind, either by slipping or with throttle modulation.  It will obviously be harder than no wind, and practice will make perfect.

Thanks Robert for the answer.  When landing on windy days here the plane can tend to sink rather than float when flying close to the runway.  This can take me off guard causing me to land well short of my spot or even causing me to bounce the landing.  I knew that headwind decreased the closer you go to the ground but the sink can be so strong sometimes I thought something else may be going on with ground effect.  Its probably just a loss of headwind like you said.  The winds here can be very gusty and brutal.

@DanielHaverporth adding a few knots to approach speed on windy days might help.  This would be a perfect lesson with an instructor and well worth it.  A little skip from being a bit fast on touchdown is much better than the "pancake" from being too slow.  Good luck!

If there is a wind gradient (decreasing wind speed with altitude) over the last few tens of feet to the ground (which there almost always is), and if the plane is descending to some degree in what you are calling the "float", rather then flying absolutely horizontally, then yes, absolutely, a headwind (gradient) will tend to subtract energy from the plane (increasing the sink rate and decreasing the float time as well as distance), and a tailwind (gradient) will tend to add energy to the plane (decreasing the sink rate and increasing the float time as well as distance.)

I practice alternating upwind/downwind landings in a closed-circuit situation on a routine basis, and I find this effect to be very pronounced.

The effects described above are not dependent on ground effect per se-- they would be be present even if you were landing on some sort of perforated sieve that created friction that slowed the horizontal component of the wind, but did not actually create a true "ground effect" in the manner that a solid surface does.

Moving on to consider actual "ground effect"-- it seems likely that a wind gradient would also, somehow, have some sort of effect on the ground effect.  How could it be otherwise?  Either the ground is altering the dynamics of the adjacent airmass, or it is not.  And any change in the magnitude of the ground effect will affect the aircraft's rate of energy loss, even in a completely horizontal "float". What the effect of the wind gradient on the ground effect would be, is not completely obvious, but it seems unlikely that it would be absolutely zero.

If you wish to state that there is no wind gradient at all in your situation, then you are essentially saying that there is no friction between the wind and the ground.  In that case, the airmass doesn't "know" anything about its speed relative to the ground-- the "ground" could actually be a conveyor belt turning hundreds of miles per hour in some arbitrary direction, and the airmass would be completely unaffected.  In such a case, naturally, the motion of the ground relative to the airmass has zero effect on the aerodynamics of the landing aircraft.  Or to put it another way, in such a case, the wind speed and direction, relative to the ground, has zero effect on the aerodynamics of the landing aircraft.  But such cases can only be hypothetical-- in the real world, there is always some amount of gradient in the speed of the wind near the ground.


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Is the steep spiral maneuver criteria in the FAA Commercial ACS Flawed?
The Commercial ACS steep spiral maneuver calls requires a pilot to fly a descending spiral with power set to idle and maintain a constant radius around a point.  The maneuver is supposed to be flown at best glide speed Vg.  You are allowed to fly up to a bank of 60 degrees to maintain the radius around the point.  You need to complete three 360 degree turns with no power and complete the maneuver at 1500 feet AGL
This maneuver is a piece of cake when flown with no wind; you just have to fly a constant bank and airspeed.  However things get much harder when there is a wind.  When you fly downwind your ground speed increases so you have to increase bank to maintain the radius and when you fly upwind you have to decrease bank to maintain your radius.  The ACS specifies that the applicant has to maintain an airspeed of +- 10 knots, a rollout heading of +- 10 degrees and complete the maneuver at an altitude of no lower than 1500 feet AGL.
Best glide in my airplane is 80 MPH.  The other day I had a 30 knot wind from the Southwest and tried flying this maneuver with the wind.  On downwind I ended up having to bank the airplane to a 45 degree angle while trying to maintain best glide.  When I did this the stall warning went off.  When you do the math you can see why.  Stall speed increases with bank angle.  The calculation for the the new stall speed at a bank angle is the normal stall speed times the square-root of the load factor which for a 45 degree bank is 1.4.  For my airplane the stall speed is 67 MPH so when you do the math, the new stall speed comes out to  79.27 MPH.  So you can see why the stall warning went off.
Best glide is really related to an angle of attack and not airspeed.  When you increase bank angle you need to increase angle of attack to prevent the airplane from going into a spiral dive.  So shouldn't you increase airspeed when increasing bank angle to maintain the best glide angle of attack?  If that is so, then you would violate the ACS standards and could fail your commercial check ride.  I also feel that this maneuver is unsafe for high bank angles (high winds) as specified as it could cause a pilot to stall the airplane in a bank and risk a possible spin.
In my opinion, I believe the maneuver should specify to maintain a constant rate of descent, allowing for changes in airspeed to maintain the best glide angle of attack.
Looking for answers from pilots and aerodynamicist on this question.

Stall speed only increases to the extent that you increase angle of attack.  Your math works if you are doing a level turn, but the point here is to dump lift to lose altitude.

Also, if you read the general instructions & description for all ground reference maneuvers, somewhere, it says you should always enter the maneuver downwind. This ensures that at the beginning of the maneuver you will be establishing the highest bank angle that you will need in any part of the maneuver. But you are right that your "best glide speed" should really be a "best glide AOA", and, if you want that,  you should establish it when entering the maneuver,  (again, downwind). But I don't believe this maneuver calls for that.

Your assumption that the steep spiral manoeuvre has to be flown at best glide speed is wrong.
Chapter 10 of the Airplane Flying Handbook (FAA-H-8083-3C) (pdf, ~6,7 MB) says on page 10-3:

The objective of the steep spiral is to provide a flight maneuver for
rapidly dissipating substantial amounts of altitude while remaining
over a selected spot.

If you want to get rid of altitude quickly flying at best glide speed is not really helpful. When you continue reading in above document it explains how you initiate the steep spiral on page 10-4:

In general, the throttle is closed to idle […] and gliding speed is
established […] the steepest bank should not exceed 60°.

See how they only mention gliding speed and not best gliding speed? You want a lot of drag (= high bank angle) so you have to pitch down to keep your speed which results in the desired high sink rate.
You are totally right – flying high bank angles increases your stall speed and you did the math. The maximum acceptable bank angle in this exercise is 60°. You surely know that for a 60° bank turn while maintaining altitude the load factor is 2.
So to be on the safe side your worst case for this manoeuvre would be a 60° bank turn while maintaining altitude. Doing the math with a stall speed of 67 mph with wings level you get a stall speed of 95 mph for a 60° bank turn (67 * sqrt(2) = 95).
So selecting a glide speed of 95 mph for the steep spiral manoeuvre would be a safe first guess.
When you check the Commercial Pilot ‒ Airplane Airman Certification Standards (FAA-S-ACS-7A (with Change 1)) (pdf, ~1 MB) you'll find the requirements for the steep spiral manoeuvre on page 35.
Under Risk Management it says:

The applicant demonstrates the ability to identify, assess and
mitigate risks, encompassing:
[…]
CA.V.B.R3 – Low altitude maneuvering including, stall, spin, or CFIT.

(my emphasis)
Selecting a safe glide speed that is higher than your best glide speed shows exactly that. You identified a risk and mitigated it.
Talk to your instructor about this. Explain your thoughts and the conclusion you came to. He or she might have other valuable input for you.


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Aspect ratio of an elliptical wing
I am looking into elliptical wings at various aspect ratios and my intuition tells me that an elliptical wing with aspect ratio of one is a circle, meaning the chord and the span will be equal. But, when I lay down the math, this is not true. For example,
$$
AR=1=\frac{span^2}{area}=\frac{span^2}{\pi (span/2)(chord/2)}
$$
$$
{\pi (span/2)(chord/2)}={span^2}
$$
$$
chord=\frac{4*span}{\pi}
$$
This tells that if the span is 100, then the chord will be 127 approximately for an aspect ratio of one, which is not a circle. Is my math correct, is an elliptical wing with an aspect ratio of one not a circle?

is an elliptical wing with an aspect ratio of one not a circle?

Aspect ratio is wingspan divided by average wing chord.
Let W = wingspan.
A perfectly square wing would have an aspect ratio of 1, because the wing chord at any point = W, and thus the average wing chord = W.
Take a perfectly square wing and draw a circular wing inside of it, with the same wingspan, and the same root chord, as the square wing.  Clearly the average wing chord of the circular wing is less than the average wing chord of the square wing, so the aspect ratio of the circular wing must be greater than 1.
If we took the circular wing and "compressed" or "compacted" it into an ellipse (with wing root larger than wing span) by pushing on the wing tips, at some point we'd eventually achieve an aspect ratio of 1.  But that wing would clearly no longer be a circle.
So no, an elliptical wing with an aspect ratio of 1 is not a circle.
What is the aspect ratio of a circular wing?
Aspect ratio = span squared / area.
Let the wingspan be equal to 1 arbitrary unit, which is twice the wing radius.  In these same units, the wing area is equal to pi times ((.5) squared) which works out to  .785.  This gives an aspect ratio of 1 / .785, which is 1.274.
PS the math in the original question is correct, as long as we keep in mind that the term "chord" is being used there in a way that actually means "root chord".

Since π is used for area but not span, the aspect ratio of a circle is 4/π. Your result is good, but presenting it as a function of π might be more revealing. Of course, the question already presents it that way.

I only answer when nobody steps forward or the existing answers are poor. So I saw no need to add my own here.

Thank you very much for your explanation, the square wing example was helpful!


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How does an Airport decide to change CAT status - what ground equipment is required for CAT I / II / III
The airport must,  of course, be continuously monitoring the status of ILS, Lighting, RVR etc.  From this status information, it seems logical that the CAT of any Approach can be calculated - but exactly what logic is used for each CAT please?
Also, does the DVOR (and HP DME) in any way affect the CAT of an Approach?

Welcome to aviation.SE! You seem to have a few different things in the title and body of your question, so you might consider simplifying it if you can. We strongly prefer to answer only one question at a time (see the [tour] for more information on how StackExchange works). This question might be helpful, even if it doesn't answer everything you're looking for.

An airport is not Cat I/II/III.  A specific approach is.
Every ILS array, every IFR-rated pilot and pretty much every IFR-equipped aircraft (even a GA pilot in a Cessna), can handle a Cat I approach.
Additional ground equipment is required for a Cat II/III approach, as well as additional crew training and aircraft equipment. For cost reasons, this is mostly limited to airlines and their hubs.
Assuming properly equipped and working ground equipment and aircraft, and a properly trained and current crew, when cleared for the “ILS”, airline crews will execute the Cat II/III version of the approach if weather or maintaining currency dictates.
If anything does not meet those standards, a crew can only execute the Cat I version of the approach.  If the weather at the airport is worse than Cat I minima, then they have to cancel or divert—something airline management doesn’t want happening at a hub, which is why they’ll spend the money making sure that doesn’t happen there.

I was under the impression that the ground controllers had to know when CAT II/III was in use so they could keep protected areas cleared.

@TomMcW They protect the critical area any time the weather is below 800-2. You only have to notify them if you need (for currency) to do a Cat II/III approach in weather better than that.

Yes, that's exactly what @Tom is saying, and it's a very good point. Our February safety briefing mentioned this. Controllers are not expecting crews to perform a CATIII approach in better-than-800-and-2 conditions and the crew should advise if they are. 7110.65 3–7–5b, and see also 3–7–5a1(b), which would not be applied in good weather unless specifically requested.


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Can I still can apply for R-ATP 1000 hour, if I get my multi engine add on under part 61?
I have completed my private, instrument rating, and commercial under part 141. Can I still able apply for R-ATP 1000 hours, if I get my multi-engine add-on under part 61?


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Is it plausible that helicopters are safer than cars?
For some reason there is a lot of talk on helicopter safety online at the moment, and one fact that keeps coming up is "helicopters are safer than cars", supported by this article "Are helicopters safe? How they stack up against planes, cars and trains".  It notes the problem that "We know the number of flight hours for airline flights and helicopter flights. We know the number of passenger miles traveled for airline flights, rail travel and (roughly) car travel." and introduces the death index, described as:

how much more likely you are to die, roughly, by traveling a similar distance in the U.S. on each mode of transportation, with airlines as the baseline. The "death index" is the number of times more likely you are to die.

This gives value of 1 for airlines (by definition), driving or riding in a car/SUV as 453.6 and Non-scheduled helicopter flights as 63.0.
A different calculation is done by the "turbulence forecast tool" company turbli which uses DOT figures (confirmed correct for cars fatalities and miles).  This gives a rate of 120 fatalities per billion passenger hours for cars, 296 for trucks and 0.88 for commercial plane, a ratio of 136 - 336, compared to the death index (based on miles) of 453.6.  This seems pretty close, and considering the speed could be counted differently depending when one "starts the watch" in the airport.
There is an article in the LA Times about the fatal accident rate particularly of the Robinson R44, and quotes a rate of 1.6 deadly accidents per 100,000 hours flown, "50% higher than any other of the dozen most common civilian models".  This is 16,000 per billion hours, and "any of the other most common civilian models" are 12,000, or exactly 100 times that of cars.  This is too different to be put down to the speed difference and how you could airport time.
Are calculations that make helicopter travel safer than cars, and only 2 orders of magnitude more dangerous than commercial air travel, credible?

Considering how heavily regulated, thoroughly trained and constantly retrained & reevaluated pilots are vs the general populace of drivers (who, in America, are generally tested once when they first get their driver's license and never tested again), it shouldn't be surprising that air travel of any sort is significantly safer than ground travel.

Your DOT numbers give you 100X greater risk in "common civilian model" helos than cars; start with that.  It seems like you're questioning the conclusion of the first article, which is based on entirely opaque data and an unknown "non-scheduled" helo flights. Is that like Part 135 helos, or all General Aviation helo flights too? Until we can see The Points Guy's methodology, there's nothing to compare to the NTSB data except his conclusion. I'm unclear what answer might be possible get here beyond what is already given from the NTSB data.

To be clear, the DOT/NTSB numbers do not have helicopter data, I have only confirmed car fatalities/mile in that.  The helicopter crash rate came from the LA times, and it is so different I thought I must be missing something.

The R-44 is a pretty light helo, with a fair number being used by low-time pilots with minimal supervision.  IF the term "non-scheduled" does in fact refer to Part 135 helo operations, then those are looking at data for larger aircraft with more supervision, higher pilot experience levels, and more regulated maintenance and operations. So it wouldn't be surprising that Part 135 accident numbers are well below R-44 and Part 91 helo numbers.  Enough to get below automobile fatality rates? Possible, but I'd have my doubts.

Why do you think they are not credible?

@DJClayworth They cannot both be credible, as they are a factor of 100 different.

This is almost certainly going to be about untangling the statistics, and not about aviation.

There was a an article in FLYING magazine many years ago where a researcher wanted to know the safest single engine aircraft, fixed wing or rotary wing, based on a probability of death of one or more occupants. You would think the 172 would come out on top, but the single engine aircraft with the lowest risk of death was the Bell 206 helicopter. A significant factor was helicopters generally crash from a hover, where there is little energy, and the disintegrating rotor bits are generally heading away from the cabin.

The Robinson R-22 and R-44 helicopters are known to have very very high accident numbers, mostly because they are operated by amateur pilots with considerably less experience than prof. helicopter pilots, due to their comparatively cheap acquisition and operation costs. So much so, that these two helicopter types are a main driver (almost 50%) of all fatal accidents in non-commerical operation. See Page 187 of the EASA Safety Review

The Points Guy article title has a disconnect with the article body, but that's typical. The title asks if helicopters are "safe", but this should include injuries not just fatalities. I always hear people say, "But in a car crash you might survive, in an airplane crash everyone dies". Which of course is not true, but I then say "I'm glad you brought up injuries" as besides the 40,000 annual deaths in the U.S. from auto accidents, over 1 million are injured enough to require medical attention. And many of these are life changing injuries. Injury numbers adds another dimension to the question.


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Do airlines use GPS for critical purposes? If so, why?
It is being reported that airlines in Finland have noticed interference with their GPS signals near Russia.  This is causing them to be unable to land at at least one airport:

Lithuanian airline Transaviabaltika said it had been forced to cancel 18 flights between Helsinki and Savonlinna in eastern Finland after the lack of GPS made it impossible to land because Savonlinna airport does not have alternative navigation equipment. (Reuters)

I know very little about planes, but I do know a thing or to about making IT equipment for important functions that can impact public safety, and one of the core rules is never to trust unauthenticated external input for a critical function.  I have always assumed that airplane IT is held to a higher standard, mostly because most IT equipment has awful security.
Is it credible that this airplane / airport combination actually relies on GPS for a safe landing?  If so, how did this happen?  We have always known GPS is hackable, they made a film about it in 1997.

Bond movies are not exactly known for technological accuracy.

@GdD Indeed, but they at least demonstrate that the possibility of disrupting this system was in the public sphere.  If anything Bond made it look harder than it really is.

Remember that there is a big difference between safety criticality and mission criticality.  Safety was not impacted by the GPS outage.

GPS is not really hackable. It can be jammed just like basically any other radio communication, but between the space- or ground-based augmentation, RAIM and cross-check with the inertial navigation there is effectively no way to make it indicate incorrect position without the system noticing.

@JanHudec Hmm.... that reminds me of this incident where Iran at least claimed to have spoofed GPS in order to trick a U.S. drone into landing at one of its airbases. This IEEE Spectrum article from 2016 also seems to suggest that GPS spoofing is a real threat.

@reirab Well, the unmanned drone even if the system detects disagreement between INS and GPS, with the control signal jammed it does not know what to do and might end up following the invalid GPS anyway. But in a plane with live pilots such disagreement should generate a loss of RNP warning and the pilots will revert to other means of navigating. Still, Lockheed must have done something dumb, because, being a US military equipment, they should have been using the encrypted P(Y) channel that Iranians shouldn't have been able to spoof.

It's routine to see Notices to Mariners (NOTAMs, only saltier) in W. Scotland, early April, warning fishermen of regions where GPS will be inaccurate for a week or so during Nato's Joint Warrior exercises

@user_1818839 Happens somewhat frequently over the Western U.S. (in the non-salty version of NOTAMs,) too.

@user_1818839 Why would GPS be inaccurate at those time periods? Is NATO regularly jamming GPS during simple exercises?

@forest Yes, at least occasionally. See this question about one of these NOTAMs.

@mbrig Interesting. So it's just for testing interference, not to try to hide their location while they do their exercises?

@forest I think we can't say unless the military decides to give out some details. Maybe they're testing their own soldiers to see if they follow the right procedures, maybe they're testing equipment, etc... Certainly if they're warning everybody in advance about the area of the exercises, they're not concerned about people knowing the general location.

Mentour Pilot covered GPS and the other kinds of navigation in great detail in How do pilots actually navigate the skies?.

@forest During exercises, it's more likely they are testing their ability to operate in the presence of hostile jamming. However this week while HMS ***** is visiting *****,  "limited jamming of GPS will take place".

GPS, or to be more accurate, GNSS is a commonly used navigational aid in aviation, especially in smaller passenger planes. Larger airliners are more likely to be also equipped with inertial navigation systems which do not rely on external sources for guidance but they need to be calibrated from time to time to maintain accuracy.
The reason for the use of GNSS systems is its good accuracy and extremely high temporal and spatial availability (system can be used pretty much any time, anywhere) in comparison to the land-based navigation systems.
Loss of GNSS or inertial navigation capability is not safety-critical in the sense that other more traditional navaids such as VOR and radar navigation usually remain available, and in the case that even those fail or are out of reach, there still is the archaic method of using the compass and map, a skill that is required from professional pilots even today.
While I'm not fully briefed in the case in question, it is obvious that the situation was problematic, because due to the problems with GPS signal, the aircraft was unable to execute RNAV procedures in the vicinity of the airfield.
As for the safety implications of this, while it may seem a huge risk, aviation procedures take into account the possible vulnerabilities of GNSS. The devices are redundant and monitor their own performance and the reliability of the signal. Should they detect any anomalies, pilots are made aware of this, and they can use other means of navigation. Pilots also monitor the information provided to them by instruments, and cross-check this with other source to verify reliability.
As the airfield in question (EFSA) apparently did not have air traffic control services provided, there was no other means available to continue safely. It is my understanding that the flight in question was not yet in approach phase. According to AIP Finland EFSA does also provide the more traditional ILS approach which does not rely on GNSS, but as there was no method to reach the initial approach fix with great enough accuracy, the flight had to turn back.
To reiterate the safety of landing using satellite navigation: even if the flight in question was already making an RNAV approach, this method is highly redundant, and unreliable/hacked signal would with almost full certainty lead to a missed approach, and return to point of departure or an alternate airfield.

Very strange. EFSA has the Linna VOR/DME (SVL) located nearby, yet the only approach chart I can find for the ILS approach to runway 12 doesn’t reference it. It says GNSS required. Why wouldn’t they include traditional VOR on the approach chart?

@Tom, are you sure it is a VOR-DME? From a couple of the AIP charts (1, 2) it appears to be a DME only.

@TomMcW the EFSA AD section 2.19
RADIO NAVIGATION AND LANDING AIDS only lists LOC, GP and DME. So there is no  VOR approved to be used for procedures at EFSA.

@randomhead Several pages I looked at listed it as a VOR/DME. If you look at the satellite photo it looks like a VOR. Everything lists it’s usage as “RNAV” though. That confuses me.

@Jpe61 I see that it’s not approved for the procedures, I’m just curious as to why. I think I’ll post it as a question.

As a pilot I do not disagree with the informative comments above, and would like to add a few additional points to ease your fears.

Pilots DO use GPS (satellite) for navigation - in concert with an assortment of other radio navigation signals such as VOR/DME stations and ADF (AM band) to constantly keep track of where they are. On board there are gyroscopes inside the Heading Indicator or the INS  that work independently without any external influence.  All aircraft can additionally be guided by air traffic control using radar. Every pilot is trained to use a compass and stopwatch if necessary. All available resources are used together and are actively crosschecked.  The pilot (or autopilot) will quickly notice if something doesn't crosscheck.

For landing, airports may offer additional lateral and vertical guidance. They range from simple light signals, to the ILS guidance, to fully-coupled automated control where the computer lands the plane. The precision is so high that the human pilot can only choose to abort the landing.  Again, all indicators are constantly crosschecked and if anything gets weird the pilot (or autopilot) will simply execute a pre-planned abort procedure called a "go around" - and try again.

With the above said, all of these navigation aids are prone to power failure, misalignment, intermittency, sabotage, and human error. Oceans and Mountains can also interfere. So there are occasions when a pilot may have limited or unreliable information.  In these situations, the pilot will not be fooled and can elect what to do. (Pilot overconfidence may then become a factor.)

In conclusion, a missing, inaccurate, or sabotaged signal (GPS or anything else) is unlikely to lead to an accident or a lost pilot.
NOTE: I believe it was the movie Die Hard II where the bad guys recalibrated the ILS at the airport so the planes would hit the ground before reaching the runway.  This only works in action movies.  And you don't really need to worry about Gen5 cell phone signals interfering with the radar altimeters either. While research has shown that some interference is possible under invalid, but conceivable, circumstances, it is very unlikely the pilot wouldn't notice discrepancies long before hitting the ground.
On your question about cyber security I know that none of the above (except maybe the CAT3 auto landing) is really prone to a crypto attack.  Pilots already factor out any signal that doesn't correlate with the others - no matter what the underlying reason is - and they are accustomed to doing so because it happens all the time.  Even simultaneously attempting to jam, misalign, or impose some denial of service attack on every signal at the worst possible time will not likely cause a crash. And such is the case with the Finnish pilots.  They noticed the discrepancies long before it was a problem.

I say this from an engineering point of view, not a flying one.  As "Pilots already factor out any signal that doesn't correlate with the others"  it would appear that interference with GPS would remove one important signal, significantly reducing redundancy and the margin for other failures.  That could mean the need to do things differently, such as divert to where conditions or equipment are more suitable.  Is that a valid conclusion for me to draw?

Your conclusion is valid, and diversion is precisely what happens - routinely.  (mostly cuz of weather) The loss or compromise of anything, navigation or other, reduces margins and confidence.  And there are rules, policies, and laws that establish certain minimums to keep an overconfident pilot from setting up a dangerous scenario, especially for passenger operations.  When minimums are not attainable, the pilot will divert to an alternate airport that should have been selected before takeoff, and should still have 30 minutes of fuel left when he arrives at the alternate.

It's not something that's absolutely needed to fly, but more advanced EGPWS units like the Honeywell Mark XXII EGPWS a terrain database and GPS as at least one of the inputs for locating the aircraft.  Normal GPWS can tell when the aircraft is approaching the ground below, but EGPWS's terrain database can prevent suddenly flying into the side of a mountain.


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Are matching/duplicate marker names on a flight plan errors and/or occurrences most systems deal with?
It is reported that Nats, formerly known as National Air Traffic Services in the UK, has explained the recent national delays on matching marker names on a flight plan:

In its initial report published on Wednesday, Nats said that at 08:32 on 28 August, its system received details of a flight which was due to cross UK airspace later that day.
Airlines submit every flight path to the national control centre; these should automatically be shared with Nats controllers, who oversee UK airspace.
The system detected that two markers along the planned route had the same name - even though they were in different places. As a result, it could not understand the UK portion of the flight plan.

From the point of view of a software developer who knows nothing about flying, it sounds like a relatively common coding error where one expects two random labels to be different and therefore uses them as identifiers, but they are the same more frequently than you expect because of the Birthday problem (or bad RNGs).  However if there is something in the specification that means such a collision should not occur then the mistake is not with the developer of the system.
What happened here?  Did someone submit an invalid flight plan that broke the system and could have broken any system?  Is it a beginner coding mistake in our national infrastructure?  Does this actually happen quite frequently and we have been dodging the bullet for five years since the system started?  Is there another explanation?

When I last checked about 3 years ago, there were 4,242 intersection names that were used more than once globally. See this answer for details.

Did someone submit an invalid flight plan that broke the system and could have broken any system? Is it a beginner coding mistake in our national infrastructure? Does this actually happen quite frequently and we have been dodging the bullet for five years since the system started? Is there another explanation?

It's none of these things, as the report states.

Did someone submit an invalid flight plan that broke the system and could have broken any system?

No, the flight plan appears to have been fundamentally valid, but unfortunately had two waypoints of the same name towards the start and the end. This meant the software was unable to plot a route and accurately cater for the flight.

Is it a beginner coding mistake in our national infrastructure?

I think it's wrong to call this is a "coding" mistake. The software was working as designed - whoever wrote the code implemented the design and intent of the software accordingly. It seems there is no in-built logical way of dealing with this that can be safely automated, but NATS acknowledge that the raising of a critical event was unforeseen.
I.e., the issue really boils down to the fact the error was unforeseen and was essentially unhandled. Because of this, the system went into a fail safe. The better approach, now the issue is understood, is to raise a flag for that particular plan for human intervention.

Does this actually happen quite frequently and we have been dodging the bullet for five years since the system started?

No, this is the first time since the software was implemented 5 years ago that this particular scenario came up. I think that fact alone, over millions of flights, explains why nobody sat down and drew this scenario up on a whiteboard

This is a good answer, but to clarify it is the first time this has happened for a route that included them IN THE UK.  It could be that this is a frequent occurrence in for example Belgium where there are 2 SIERAs only 18.5 NM away from one another as per the answer linked in a comment.

Another interesting point would be if these two waypoints were both allocated their names by the UK aviation authority.

@User65535 Those two SIERAs are VFR points, so they wouldn't be on an IFR flight plan. In general, I'd guess most duplicate names come from either VFR points or points on procedures (SID/STAR/Approach), which are also not part of the IFR flight plan (the plan just contains the procedure name, if at all).

I'm afraid that this isn't an aviation question, it's more of an IT question and a hard one to answer as the systems involved are proprietary.
I am a software engineer myself, almost 15 years now, half of them in the development of aviation software -yet not safety critical. I will try to address the main question regarding the duplicate marker names.
Uniqueness of waypoints
Waypoints that are expected to be unique within the airspace system under consideration according to
ICAO ANNEX 11 – AIR TRAFFIC SERVICES
APPENDIX 2. PRINCIPLES GOVERNING THE ESTABLISHMENT AND IDENTIFICATION OF SIGNIFICANT POINTS Paragraph 3:

3. Designators for significant points not marked by the site of a radio navigation aid
3.1 Where a significant point is required at a position not marked by the site of a radio navigation aid, the significant point shall be designated by a unique five-letter pronounceable “name-code”. This name-code designator then serves as the name as well as the coded designator of the significant point.
3.4 The name-code designator assigned to a significant
point shall not be assigned to any other significant point.

There are other paragraphs as well but these 2 are the important ones to know that the point uniqueness is mandated.
You might be wondering then "how did the 2 SIERAs come that close in Bianfable's answer"? If you have a look at the Belgian AIP then you will see that the 2 waypoints have a different parent. The point at northwest belongs to EBST SINT-TRUIDEN / Brustem and the point at southeast belongs to EBLG/ Liège airport.
When a VFR flies within the area of EBLG and they are in contact with the tower and ATC instructs them to "report SIERA" there is no way to confuse it with the "other" SIERA. The "context" is the airport and the waypoints are unique within their context. Finally, please note that these 2 points are VFR; they will never appear in an IFR flight plan like the one in question.
As you can see, while uniqueness can be maintained within the same context, when you "merge" the contexts together like it happens with long distance flights, it's not guaranteed that you will not get any duplicates. As a result, you would expect that a system handling such data would be able to deal with duplicates. Still, it's not black or white.
What could have gone wrong
Unfortunately we can't tell for sure. We are lacking important information like the raw flight plan, the waypoint names and their locations. Also I don't work neither for NATS nor Frequentis that developed the system so I don't have inside information.
I read the report that Dan linked and there are things that need further clarification. Read page 9 and you will see what I mean. One of these points is:

Next, it searches backwards, from the end of that section, to find the UK airspace exit point.

This confuses me. There is no need to search backwards unless you want to compute the 3D trajectory of a descending flight and that can be done in a subsequent state for simplicity. Once you find the first point in the FIR, then you can move forward until you find the first foreign point. Granted, as DeltaLima correctly pointed out in a comment, a flight might exit the FIR and enter back again later on. In any case I would expect the system to not quit after finding the first exit point but make sure that the rest of the points are irrelevant. Can be done in direct or reverse order.
I don't say that I know better than them. But I feel that the wording in the report is (overly?) simplified and that there is certainly more than meets the eye.
On page 6:

The FPRSA-R sub-system exists to convert the data received from IFPS (in a format known as ATS Data Exchange Presentation, ADEXP) into a format that is compatible with the UK National Airspace System (NAS)

But later on

The flight plans delivered to FPRSA-R by IFPS are converted from an ICAO document 4444 (ICAO4444) format to a format known as ADEXP.

Again I'm confused. The first statement implies that FPRSA-R receives plans from IFPS in ADEXP format and and in the second statement in ICAO format. That might seem trivial but things can be lost or taken wrong in translation.
Moreover, according to the same report, IFPS handled the same flight plan without issues so it could not have broken any system; it was tried and it didn't.
Last but not least, we need to have access to the problematic data and as far as I see the flight plan has not been published up until this moment. This is important as according to the same report, the system has processed successfully 15 million flight plans up until now. I find it hard to believe that this was the first time that the system encountered a plan with duplicate points. I might be wrong though as the airlines might be vetting the flight plans, just to be on the safe side. I don't know that for sure.
The most important question that I feel it needs to be answered by the relevant parties (not by anonymous people on the internet) is why a single faulty input resulted in taking out both their main and the backup systems.
We certainly need more information in order to avoid speculation.

Hi Stelios, the reason for doing a backward search from the end, instead of a forward search from the point of entry, may be related to the possibility of a flight leaving UK airspace and then re-entering it. By searching backwards from the end, you are sure to have the segment between the first entry and the last exit.

Regarding the conversion: your interpretation of the quote is incorrect: the IFPS converts the ICAO flight plan to ADEXP before forwarding it to the UK FPRSA-R. The wording in the report would perhaps better be: The flight plans delivered to FPRSA-R by IFPS *have been* converted from an ICAO document 4444 (ICAO4444) format to a format known as ADEXP.

My suspicion is that the FPRSA-R system allows for flightplans that have the same waypoint multiple times in the route (e.g. for accommodating a surveillance flight do multiple rounds). To reduce the load on the aeronautical database, the coordinates of each waypoint are queried only once per flight plan and are locally cached during the flight plan's processing. If the coordinates for a named waypoint are already in the cache, there is no need to ask the database again. That logic only works if duplicate waypoint names within the plan are refering to the same geographical position.

(1/2) @DeltaLima Hello Douwe, good to hear from you after all this time. :) Regarding comment 1: I updated the answer though I believe the order isn't relevant. Regarding comment 2, that's exactly my beef. The wording leaves room for misunderstanding and the report seems to be targeting a broader audience and not just niche. It could have been more carefully worded. In my humble opinion. Regarding comment 3, I still believe that it's too obvious a case to miss. Unless it's the first one after the 15 million where name1 = name2 and location1 <> location2.

(2/2) Then what can I say. Perhaps the 4000+ duplicate points on the planet are not enough to create that condition more than once in 15 million. Regardless, what you are describing is caching and allow me to believe that this isn't the case: the algorithm processing the plan should be oblivious of how the points are accessed. It should be able though to know which point to retrieve. Both of them are said to be outside the UK FIR so I doubt it if they are in the aeronautical database.